Conventionally, a vehicular electronic device is installed in a vehicle compartment and electromagnetic noise radiated from the electronic device is interrupted by a vehicle body serving as a shield and hence does not affect an antenna adversely that is attached on a roof of the vehicle body.
In recent years, techniques for sensing a vehicle surrounding situation becomes considered as important, as techniques used for autonomous driving, drive assistance or the like, and it is increased to mount electronic devices for sensing outside a vehicle compartment. This is associated with a drawback that when an electronic device (e.g., camera) is installed near the vehicle antenna, electromagnetic noise radiated from the electronic device etc. is received by an antenna to cause reception trouble in a radio, a TV receiver, etc.
A specific vehicular antenna device incorporating a camera module as an electronic device will be described using FIGS. 20 and 21. A vehicular antenna device 100 shown in FIG. 20 is equipped with an antenna element 103, an antenna amplifier board 104, and a camera module 110 which are disposed in a space surrounded by an antenna base 101 and an antenna case 102. The camera module 110, which serves to take a moving image and/or a still image of, for example, a scene behind the vehicle body, has a configuration shown in FIG. 21. That is, the camera module 110 is equipped with a lens 111, an image sensor unit 112, a video signal output unit 113, an oscillator 114, and a power unit 115 for supplying electric power to the individual circuit units in such a manner that they are disposed in a camera module case 120. A module cable 121 (including a signal line and a power line) which is connected to the camera module 110 passes through an attachment hole of a vehicle body roof R to which the vehicular antenna device 100 is attached and is connected to connection targets 125 such as a battery, a monitor, and an operating panel. An antenna cable 105 which is connected to the antenna amplifier board 104 also leads to inside the vehicle compartment through the attachment hole of the vehicle body roof R.
The principle according to which noise is generated in this case will be described. When the camera module 110 is powered on, a voltage +12 V supplied from the vehicle needs to be converted into voltages (e.g., +3.3 V) to be used inside the module. Noise is generated by a switching regulator of the power unit 115 in the process of this voltage conversion. Noise is also generated by the oscillator 114 which is provided inside the module and allows the image sensor unit 112 to operate. That is, the power unit 115 and the oscillator 114 also act as noise sources and noise propagates through lines that connect them to the other circuit units. Resulting noise is radiated to the outside passing through the case 120. Furthermore, noise is radiated from the module cable 121 which includes the signal line and the power line. That is, there are two general noise radiation (transmission) paths: one is a path of radiation from a circuit board (mounted with the image sensor unit 112 to the power unit 115) of the camera module and the other is a path along which noise is radiated as it propagates through the power line, the signal line, etc. of the module cable 121.
In the vehicular antenna device 100 shown in FIG. 20 in which a condition is established that the antenna element 103 and the camera module 110 as an electronic device are close to each other, noise that is radiated from the circuit board of the camera module 110 is received by the antenna element 103 to interfere with an audio signal and an image signal of a radio, a TV receiver, or the like that should be received properly. Likewise, noise that is radiated from the power line, the signal line, etc. which are connected to the camera module 110 is received by the antenna element 103 to interfere with a signal that should be received properly.
The following Patent documents 1 and 2 are known as describing a vehicular camera device.